The invention relates to a rotary drill bit and more particularly it relates to a drag type rotary drill bit equipped with cutting elements positioned on wings.
Conventional drag type drill bits are commonly provided with nozzles which discharge into waterways in front of the wings and which direct high velocity mud jets in a direction orthogonal to the borehole bottom. A disadvantage of this known arrangement is that in some formations drill cuttings are removed to an insufficient extent from the region of the cutting elements, thereby causing overheating of the elements and reduced drilling progress.
Numerous attempts have been made to improve the cleaning and cooling performance of mud jets. U.S. Pat. No. 2,365,941 discloses a bit provided with nozzles which direct the high velocity mud jets in a substantially parallel direction relative to the cutting elements of the bit and to the borehole wall. U.S. Pat. No. 4,116,289 discloses a bit provided with nozzles which direct the mud jets towards the front face of the cutting elements of the bit in such a manner that the jets strike said front faces at an acute angle.
Although the known arrangements generally enhance the cleaning and cooling performance provided by the mud jets, it was found that removal of drill cuttings sometimes stagnated, particularly in shaly formations.